Jokes aside, to expect a bull run to start next April 2024 means the market would be in a warming stage due to the halving which is going to happen on the following month, May. That is a possibility, but we don't have any guarantees. It's purely a speculation, like any other. The bull run can start on the pre-halving period, during halving period or post-halving period. It will depend on the global economical scenario as well.
Bitcoin price bullishness can start at any time, that's true but it has to be supported by solid foundations. Global economic issues including inflation and interest rate adjustments may have a positive/negative impact on bitcoin price movements during the pre halving. But anyway, I believe it will be bullish after the halving.
There is no way to keep the bitcoin network safe from 51% attacks if big mining company drop out regularly because their income doesn't match their expenses. Mining costs have increased, while the reward they get from each block has been halved, so only a bullish scenario will help them keep operating normally after the halving.